--> --> Abstract: Mapping the Northern South Atlantic Continental-Oceanic Boundary: Rift to Early Drift Along Extensional and Strike Slip Margins, by Steven G. Henry, Naresh Kumar, Al Danforth, Peter Nuttall, and Sujata Venkatraman; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Mapping the Northern South Atlantic Continental-Oceanic Boundary: Rift to Early Drift Along Extensional and Strike Slip Margins

Steven G. Henry1; Naresh Kumar2; Al Danforth2; Peter Nuttall3; Sujata Venkatraman3

(1) RIFTT, Las Cruces, NM.

(2) Consultant to ION/GX Technology, Houston, TX.

(3) ION Geophysical - GX Technology, Houston, TX.

Based on newly acquired deep imaging Pre-Stack Depth Migrated (PSDM) seismic data (Greater BrasilSPAN) for the northeast and northern margins of Brazil, we present a new map of the continental oceanic boundary (COB). We compare this COB to the African conjugate margins, where the COB has been mapped using GXT AfricaSPAN data. These maps allow us to match segments of extensional and strike slip crustal movements. The margins north of the salt basins appear to be underlain by thick (>40 Km) continental crust that was abruptly broken in the last stage of the opening of the South Atlantic.

In the central portion of the South Atlantic where the salt basins developed, is primarily a zone of crustal extension. Valanginian pre-salt sag basins contain rich source rocks responsible for the recent giant discoveries (Tupi Play). The seaward edge of the sag basin was subsequently faulted (diachronous rifting) in the Barremian, and the younger syn-rift filled with volcanics and salt as the continents separated.

The northern South Atlantic (Potiguar- Foz do Amozonas) margin is primarily strike slip. Pre-breakup basins are less well developed, due to the underlying thick crust. Recent discoveries along the African conjugate margin (Jubilee in Ghana , Venus in Sierra Leone) were sourced from rocks in the pre-rift (Albo-Aptian) and above the Aptian breakup unconformity in the early syn-rift restricted basins that developed on the ramps between the strike slip faults.

Using the “tight fit” reconstructions based on the Brazilian “nose” fitting into the Nigerian “notch”, the northeastern margin of the South Atlantic (Brazil: Paraiba to Sergipe-Alagoas, Africa: Cameroon to Northern Gabon) consists primarily of numerous smaller displacement strike slip faults with minor extensional segments. To the south, in order to close the South Atlantic between southern Gabon and the Reconcavo to Jequitinhonha basins (Brazil), a large displacement strike slip system is needed that begins just north of the offshore Gabon gravity low (thick crust).

Through the mapping of the COB on over 100,000 Km of deep imaging PSDM seismic data in the South Atlantic, the timing and positions of the continental blocks have been estimated during the magnetic “Quiet Zone” for which only extrapolated age of ocean crust have been previously available. Understanding the role of extensional and strike slip segments is shown to be an important component for estimating source rock deposition and maturation.